Hyperandrogenism is a core feature of polycystic ovary syndrome (PCOS). PCOS is associated with reproductive abnormalities that include accelerated gonadotropin-releasing hormone (GnRH) release, LH excess, oligo- or amenorrhea, arrested ovarian follicular maturation, and development of follicular cysts. Clinical and animal studies have provided evidence that hyperandrogenism contributes to the manifestation of these abnormalities by inducing resistance to steroid negative feedback of pulsatile GnRH release. Little is known, however, about the neuronal mechanisms, including steroid receptors, signaling pathways, and neuronal populations, that mediate the negative feedback actions of estradiol and progesterone in the hypothalamus of female primates. Moreover, the pathogenic mechanisms by which androgens impair neuronal responsiveness to estrogen and progesterone feedback remain obscure. Project II studies will make use of viral vector-mediated gene silencing and a validated nonhuman primate model of androgen-induced reproductive PCOS phenotypes to address these major gaps in our understanding of the mechanisms that mediate the pathogenesis of PCOS. Using these methods, we will directly test the hypotheses that 1) estrogen receptor alpha (ERa) in hypothalamic arcuate nucleus (ARC) neurons mediates physiological negative feedback in the rhesus macaque, 2) androgen excess attenuates estrogen-induced-expression of progesterone receptors A and B (PR A/B) and confers resistance to negative feedback actions of estradiol and progesterone, and 3) reduced PR A/B expression in the ARC recapitulates the reproductive abnormalities of PCOS. These studies will thereby establish the normal physiological receptors and target cells that mediate steroid negative feedback in a primate, identify androgen-induced resistance to estradiol and progesterone actions as a fundamental pathological mechanism underlying PCOS-like reproductive dysfunction, and directly test the validity of the concept that hypothalamic resistance to progesterone is a determinant of reproductive abnormalities in PCOS.